1. Field of the Invention
This invention relates to gas sensor operating systems in general and more particularly to exhaust gas sensors operating in a fuel injection system for determining when the operating temperature of the sensor is within its normal operating range.
2. Description of the Prior Art
In a preferred embodiment wherein an oxygen gas sensor is positioned in the exhaust system of an internal combustion engine for generating an output signal for controlling the air fuel ratio of the fuel mixture supplied to the engine, the sensor must be above a certain temperature in order to operate properly. If the oxygen gas sensor is below this temperature, the sensor operation is abnormal resulting in the internal combustion engine operating unsatisfactorily.
When an oxygen gas sensor in the exhaust system is operating below its operating temperature typically after a cold start or during a prolonged idle condition, its impedance is or will become very high. However during normal temperature operations its impedance decreases to a low value.
Several prior art control systems are used to control the output of the exhaust gas sensor circuit during the cold operation. One control system disables the output of the exhaust gas sensor when the engine coolant temperature is below a predetermined temperature level. In this system it is assumed that when the engine coolant temperature becomes sufficiently warm, the exhaust gas temperature is sufficiently high to heat the oxygen gas sensor to its operating temperature.
Another system is based strictly on a time signal. The timing circuit is initiated from the turn on of an ignition key and at the end of the predetermined time it is assumed that the exhaust gas sensor is at its operating temperature. The disadvantage of this particular system is that the time is an arbitrary value and is not able to cover all engine operations. In particular, in either of the above two systems if the internal combustion engine is operated at an idle condition for a sufficiently long period of time the operating temperature of the sensor would decrease and yet neither of the two systems would be able to detect the sensor temperature decreasing.